Myth: an elevated leukocyte count distinguishes septic arthritis from less serious causes of hip pain.

Abstract

Pediatric septic arthritis of the hip is a feared disease in children who have a limp because of the devastating consequences if it remains untreated. One of the most difficult challenges that clinicians face today is differentiating between an infected hip and other less serious causes of hip pain, such as transient synovitis. It has been shown that early diagnosis and aggressive treatment of an infected hip can substantially reduce the risk of complications, such as osteomyelitis, persistent hip pain, shortening of the limb, avascular necrosis of the femoral head, and even death. In fact, Klein et al found that the institution of intravenous antibiotic therapy and hip drainage and irrigation within 4 days of the onset of symptoms was one of the most powerful predictors of a satisfactory outcome.1 The diagnosis of septic arthritis will not be missed in patients who present with hip pain; a toxic appearance; a high temperature; and a hot, swollen joint. However, when children present in the early stages of their disease, clinical signs may be subtle, and reliance on laboratory values often becomes central to decision making. Obtaining a percutaneous specimen of the joint fluid for cell count, Gram's stain, and culture is the gold standard for making the diagnosis, but it is invasive and often requires general anesthesia to perform. A complete blood cell count is easy to obtain, and an elevated leukocyte count has traditionally been considered a sensitive indicator of serious infection. Therefore, many clinicians have tried to use this test to differentiate between septic arthritis of the hip and transient synovitis. Several studies have shown, however, that the peripheral white blood cell count is an unreliable marker of septic arthritis in children and should not be used to rule out disease.